• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.42-46
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• 2002

The solidification cracking susceptibilities of Al-Mg-Si alloy laser welds were assessed using the self-restraint tapered specimen crack test. The cracking susceptibility of 6061 and 6082 Al-Mg-Si alloy laser welds was substantially reduced when the filler wire containing high Si such as Al-12 wt.% Si (4047A) was used. The amount of eutectic was observed to affect the solidification cracking of Al-Mg-Si alloy laser welds. Abundant eutectic seems to heal the cracking and reduces the cracking susceptibility, while an initial increase in eutectic liquid leads to the increased cracking tendency.

• Journal of the Korean Society for Nondestructive Testing
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• v.2 no.1
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• pp.10-16
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• 1982

This study was carried out to measure the flaw height of welds in consideration of the effective probe angle in ultrasonic oblique detection. Specimens with inserted artificial flaws were made and flaw heights were estimated from detecting these specimens. Two different methods were applied to estimate flaw heights. From the result of the experiment, flaw height could be measured within the accuracy of 15% percent error and the difference between the probe distance method and beam path method is about 5% relatively small. It is considered that the results obtained this experimental study could be helpful informal ions for measuring flaw height.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.101-105
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• 2001

Due to their elastic anisotropy, ultrasonic testing of austenitic welds, frequently used in nuclear power plants, is much more difficult than that of isotropic elements. For accurate testing of austenitic welds, ultrasonic wave phenomena therein must be full understood. This study uses an accurate and effective numerical model, the mass-spring lattice model, for such phenomena. By comparing the numerical results with the corresponding analytical results, it is shown that the model is capable of accurately predicting the generation, reflection, refraction, and scattering phenomena of ultrasonic waves in anisotropic austenite welds. Therefore, the mass-spring lattice model will provide a very useful tool for simulating ultrasonic testing of austenitic welds, and thus will contribute to the enhancement of reliability of such ultrasonic testing.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.98-104
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• 2002

A study on microstructures of welds for Zircaloy-4 sheath end closure by the resistance upset welding methods was carried out. Two upset welding process variations such as magnetic farce and multi-impulse resistance welding were used. Grain size and microhardness across welds were analysed in terms of welding parameters. Magnetic farce resistance weld with one cycle of unbalanced mode has smaller upset length and $\alpha-grain$ size in heat affected zone than those of multi-impulse resistance weld because of lower heat input and shorter welding time. Heat affected zone formed by two upset resistance welding variations revealed fine Widmanstatten structure or martensitic ${\alpha}'$ structure due to the high heating rate and foster cooling rate. Magnetic force resistance welds showed recrystallized grains before grain growth, whereas multi-impulse resistance welds showed full grain growth.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.5
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• pp.427-435
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• 2008

Inspection of dissimilar metal welds using phased array ultrasound is not easy at all, because crystalline structure of dissimilar metal welds cause deviation and splitting of the ultrasonic beams. Thus, in order to have focusing and/or steering phased array beams in dissimilar metal welds, proper time delays should be determined by ray tracing. In this paper, we proposed an effective approach to solve this difficult problem. Specifically, we modify the Oglivy's model parameters to describe the crystalline structure of real dissimilar metal welds in a fabricated specimen. And then, we calculate the proper time delay and incident angle of linear phased array transducer in the anisotropic and inhomogeneous material for focusing and/or steering phased array ultrasonic beams on the desired position.

• Journal of Welding and Joining
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• v.21 no.5
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• pp.540-546
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• 2003

Recently Al alloys are being used gradually for structural materials of transports. In welding of Al alloys used for transports, good weldabilities as well as adequate mechanical properties of the welds should be ensured as structural materials. In this study, the welds formation, macro and microstructural characteristics, generation of defects and hardness distribution in welds of Al alloys of 5083, 6N01 and 7N01 by DCSP- and AC-GTA welding process, were investigated. The deeper penetration was obtained in all welds of the alloys by DCSP-GTAW with He gas, compared with those by using AC-GTAW. The 6N01 alloy showed high susceptibilities to solidification cracking in weld metal and liquation cracking in HAZ of the welding beads of both DCSP- and AC-GTAW process. The cracking ratio of 6N01 alloy was increased with increasing of welding current. The porosity ratios in weld metal of all alloys used were extremely low including all welding conditions of DCSP-GTAW. However, in AC-GTAW process, the porosity ratios of the welds using Ar gas showed much higher values than those using He gas.

• Journal of Advanced Marine Engineering and Technology
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• v.11 no.2
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• pp.71-81
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• 1987

Nowadays, the high development of industrial technique demands the optimal design of marine structures to be welded under the water, because the underwater welding of the ship hull and marine structures can decrease manpower and cost of production. However there is not available at present any report on fatigue behavior about underwater welded joints. In this paper under tention- tension repeated fatigue stress with frequency of 10 cycles per second by local controlled system, the fatigue strength properties of underwater welded joints of SM41A-2 Plate-to-Plate of 10 mm thickness were experimentally examined. The results obtained were as follows : 1) The fatigue strength of underwater welded joints of SM41A-2 was peaked at the heat input of about 1, 400 joule/mm(180 A, 36 V), while, at the heat input of more than about 1, 100 joule/mm (160 A, 33 V) that of the underwater welds at the higher than cycle of life rather than the lower cycle was higher than that of the base metal but lower than that of the atmosphere welds on account of both cooling and notch effects. 2) The fatigue limit of underwater welds increased with an increase of heat input resulting in a peak of that at the heat input of about 1, 400 joule/mm and then decreased gradually. 3) The fatigue strength at N cycles was peaked between the heat input of about 1, 400 and 1, 700 joule/mm where the strain was rapidly increased. 4) It was confirmed that the optimal zone of heat input condition for obtaining the underwater welds fatigue strength higher than that of the base metal exists, and if out of this zone, the fatigue strength of the underwater welds was lower than that of the base metal because of lack weld penetration, inclusion of slag, voids, etc. 5) By the fatigue test, the underwater welds fractured brittly without visual deformation, so the strain was remarkably less than of the atmosphere welds. 6) The fatigue life factor was peaked at the heat input of about 1, 600 joule/mm (200 A, 36 V) at which the mean strain is a little higher than that of the base metal but quite lower than those of the atmosphere welds, resulting in good underwater welds because both fatigue strength and ductility of the underwater welds are higher than those of the base metal at such heat input.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.74-83
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• 2002

In order to investigate the hot cracking phenomena of the Inconel 690 overlay welds, the hot cracking test(modified Varestraint test) was performed by varying augmented strain and welding speed in GTAW. A total of five kinds of specimens was used in the hot cracking test. The specimens used were two kinds of one layer specimens that were composed of just Inconel 690 deposited metal and three kinds of double layer specimens that were composed with as upper part of Inconel 690 weld metal and lower part of SA508 cl.3 or STS 309L. The main results are as fo11ows: In the welds composed of just Inconel 690, as the augmented strain was more increased and the welding speed was more decreased, the extent of cracking was more increased. And these cracks were mainly solidification cracks, and liquation cracks were also observed partially in HAZ. And hot cracking susceptibily of Inconel 690 welds by using filler metals containing Nb were higher than that of the welds with Nb free. The hot cracking susceptibility of Inconel 690 weld metal was increased with dilution of SA 508 cl.3 and STS 309L, and the influence of SA 508 cl.3 was higher than that of 575 309L. The results of calculation of $TSC\Delta$ and $TLC\Delta$ in Inconel 690 weld metal changed by dilution with base metal or neighboring welds were agreed well with the results of hot cracking test in this study. Therefore, it was expected that the hot cracking was considerably decreased or prevented by using proper welding conditions such as lower heat input, filler metals, base metal and neighboring welds.

• Journal of Welding and Joining
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• v.21 no.1
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• pp.5-7
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• 2003

• Journal of Welding and Joining
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• v.20 no.6
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• pp.746-747
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• 2002